1. Field of the Invention
The invention relates to a method of converting slags derived from nonferrous metallurgy, in particular primary and secondary Ni and Cu metallurgical slags, while recovering and/or enriching the nonferrous metals and forming synthetic pozzolans.
2. Description of Related Art
Metallurgical slags containing Ni, Cu and Co occur primarily in nickel metallurgy. Fayalitic Ni metallurgical slags, generally, contain 1% by weight Ni, 0.7% by weight Cu as well as 0.25 Co. The slags occur as acidic slags, their basicities CaO/SiO.sub.2 usually ranging between 0.1 and 0.4. Basically, such slags are suitable for the production of synthetic blast furnace slags upon addition of lime, yet direct use does not appear practicable on account of the high content of nonferrous heavy metals.
Oxidic slags occur not only in nonferrous metallurgy but, for instance, also in waste incineration or in the combustion of car shredder light fractions. Even those slags in most cases contain relatively high portions of nonferrous heavy metals.
EP-A 801 136 already suggested to work up oxidic slags of different origin and different contamination with heavy metal oxides or toxic substances by reducing the same above a metal bath containing an iron alloy. In that context, iron, iron-nickel, iron-copper or tin alloys were proposed as metal baths, wherein the redox potentional by the addition of aluminum, FeSi or carbon was adjusted such that FeO from the slag was metallically reduced to Fe not at all or only partially. The high admixtures of carbon regularly required in that connection presupposed the use of a high-quality coal, the metal bath having had to be adequately enriched with carbon. The submerged tuyeres required in this connection are relatively complex, calling for more or less sophisticated cooling means, since strongly exothermic reactions are being observed as carbon and oxygen are blown into iron alloys.